The present invention generally relates to communications with the long-term placement of downhole completions equipment. More particularly, the present invention relates to an apparatus and method to wirelessly communicate with downhole completions equipment. More particularly still, the present invention relates to methods and apparatuses to wirelessly communicate with and generate power for downhole completions equipment, particularly those permanently installed in the well.
Because of the variety of sensor and measurement devices used in oilfield drilling and production operations, various communication systems and schemes are often necessary. One form of communications that continually challenges the industry relates to the communication between surface and downhole equipment. Particularly, it is often necessary to retrieve data from downhole equipment and sensors for processing and decision-making at the surface. Operations such as drilling, perforating, fracturing, drill stem or well testing, and hydrocarbon production require measurements of downhole pressures and temperatures at various depths of investigation. Furthermore, communication from the surface to downhole sensors is often desired as some sensors or downhole tools accept commands from the surface to direct their operation.
One aspect of downhole communications that necessitates further innovation and invention involves the communications between surface equipment and downhole “smart” completions equipment. Completion generally refers to the process by which a drilled wellbore is “completed” or prepared to produce hydrocarbons therethrough. Typically, the completions process follows drilling, casing, and perforating operations undertaken to reach the subterranean reservoir. Thereafter, completions usually involve the installation of at least one string of production tubing, various packer assemblies, and other downhole tools (such as valves, nipples, and pumps). The packers serve to isolate one or more production zones from other portions of the wellbore depth while the production tubing serves as a conduit to carry the hydrocarbons from the isolated zone to the surface.
Additionally, the phrase “smart completions” generally refers to the placement of downhole measurement devices, usually temperature and pressure sensors, to monitor the production of the reservoir. The data from the smart completions equipment is evaluated at the surface so that decisions can be made regarding production methods and techniques in order to maximize the lifetime and productivity of the well. Because completions equipment is expected to last the entire life of the well, smart completions systems capable of lasting upwards of 15 years are necessary. Therefore, systems that rely on batteries or other stored power devices are generally not sufficient for the life of smart or other permanent completions systems. Currently, the monitoring of smart or permanent completions equipment is periodic in nature but this is subject to change as more detailed and complex measurements are enabled. Therefore, there is a long-felt need in the industry for a long-term, permanent, communication system for smart or permanent completions devices.
Accurate and reliable downhole communication is necessary when transmitting and processing complex data or data from several sensors simultaneously. For these operations, digital communication schemes are often preferred since they have improved reliability and readability over analog signals. A digital communication, one typically consisting of strings of 0s and 1s, is more reliably read and verified on the surface than it's analog counterpart. However, for digital communications to be possible between downhole sensors and surface equipment, advanced electronics, those capable of turning the analog temperature and pressure measurements into digital data streams, are needed. As the amount of data processing increases downhole, so do the power demands of such equipment. For this reason, a system to deliver power to downhole completions equipment is also highly desirable. Most desirable of all is a system to perform digital communications and transfer power between downhole sensors and surface equipment.
Formerly, direct wireline connections were used to transfer power and communications data between the surface and the downhole location. While much effort has been spent on wireline communication, its inherent high telemetry rate and power transmission capacity is not always needed and very often does not justify the high cost of deploying and installing thousands of feet of permanent or temporary wireline in a wellbore.
Additionally, acoustic and electromagnetic wave telemetry has been explored whereby a conduit containing a transmission medium is deployed to a depth of investigation. While such systems are promising, they suffer from similar cost problems resulting from their short or long term placement. Among those techniques that use liquids as medium are the well-established Measurement While Drilling (MWD) techniques. A common element of the MWD and related methods is the use of a flowing medium, e.g., the drilling fluids pumped during the drilling operation. This requirement however prevents the use of MWD techniques in operations during which a flowing medium is not available.
In recognition of this limitation various systems of acoustic transmission in a liquid independent of movement have been put forward, for example in U.S. Pat. Nos. 3,659,259; 3,964,556; 5,283,768 or 6,442,105. Most previously known approaches are either severely limited in scope and operability or require downhole transmitters that consume large amounts of energy.
It is therefore an object of the present invention to provide a communication system that overcomes the limitations of existing devices to allow the communication of data between a downhole location and a surface location.